I book my travel on Expedia. They pull up routings that don't show up on either the AA or US sites, often with prices below what I can find on the airline websites themselves.

FWIW, even before the merger I learned that the AA site was selective in what it shows. The Expedia option, for example, has in the past uncovered for me AA-numbered codeshares on other airlines that didn't show up on the AA website.